This invention relates to crystalline aluminosilicate zeolites, particularly to faujasite type zeolites and more specifically to rare earth exchanged faujasetic crystalline zeolites, preparation thereof and use as a catalyst particularly as a cracking catalyst.
Rare earth exchange crystalline zeolites have been prepared by prior art methods which generally involve ion exchange procedures in which the introduction of the desired rare earth metal into the zeolites is accomplished by a conventional single step, such as disclosed in U.S. Pat. No. 3,595,611. The latter rare earth exchanged zeolites possess catalytic activity and selectivity particularly when utilized as a cracking catalyst component.
As a result of this invention, it has been found that novel rare earth exchanged crystalline aluminosilicate zeolites having superior catalytic properties compared to other prior art rare earth exchanged zeolites, can be prepared by an ion exchange method which incorporates the rare earth into the zeolite in a multi step, particularly a two step manner. We have discovered that if the desired amount of the rare earth metal is introduced into the zeolite via a unique two step exchange procedure, the resulting zeolite exhibits an unexpected high degree of catalytic activity and good selectivity, particularly highly improved coke selectivity.